Hi. i was to trying login into account but whenever login button is pressed the appl forces to close and opens up again.

class LoginActivity : AppCompatActivity() {
    var mAuth: FirebaseAuth? = null
    var mDatabase: DatabaseReference? = null
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_login)
        mAuth = FirebaseAuth.getInstance()
        loginbutton.setOnClickListener {
            val email = emailloginET.text.toString().trim()
            val password = passwordloginET.text.toString().trim()
            if (!TextUtils.isEmpty(email) || !TextUtils.isEmpty(password)) {
                loginUser(email, password)
            }
            else {
                Toast.makeText(this, "Sorry, login failed!", Toast.LENGTH_LONG)
                        .show()
           }
        }
    }
    private fun  loginUser(email: String, password: String) {
        mAuth!!.signInWithEmailAndPassword(email, password)
                .addOnCompleteListener {
                    task: Task<AuthResult> ->
                    if (task.isSuccessful) {
                        val currentUser = mAuth!!.currentUser
                        val userId = currentUser!!.uid
                        mDatabase = FirebaseDatabase.getInstance().reference
                                .child("Users").child(userId)
                        val username = email.split("@")[0]
                        val dashboardIntent = Intent(this, DashboardActivity::class.java)
                        dashboardIntent.putExtra("name", username)
                        startActivity(dashboardIntent)
                        finish()
                    }else {
                        Toast.makeText(this, "Login Failed", Toast.LENGTH_LONG)
                                .show()
                    }
                }
    }
}